I see. That is a valid concern. Though it feels unfair to say that headscale is ‘made by a tailscale employee’. From what I understand, one of the main contributors of headscale was hired by tailscale, though he is not the only maintainer and does not own the repo from what I can tell. Still, Tailscale could decide to cede all support of headscale and that would likely hurt the project a lot. In the same way however nebula could decide to switch to proprietary licenses and discontinue their open source offerings.
It can be on your home network, but it needs to be reachable via HTTPS through the internet. So yeah, a vps is probably the best option.